1. Technical Field
The present invention relates to an optical device for multiplexing/demultiplexing optical wavelength signals, comprising phased array waveguide devices.
The present invention also relates to a phased array waveguide device for application in the optical device.
2. Prior Art
Such an optical device is known from EP-A-0 591 042. The known optical device is a multiplexer/demultiplexer device for one or more optical wavelength signals and is applicable to optical communications systems and optical switching systems. The known optical device is used in particular for splitting and inserting optical wavelength-multiplexed signals. The same optical device in the form of a phased array waveguide grating device is used to perform both multiplexing and demultiplexing operations and so the wavelength characteristics of the multiplexer and demultiplexer are well matched. The provided optical device output signals are narrow band, because the optical signals are passed through the same device several times. In addition splitting losses and noise components of the optical output signals are said to be minimized in the known device. However due to temperature variations and temperature differences of device components, transmission properties of the known optical device, such as distortion and throughput as a function of temperature in the short and long run are poor.
Therefore it is an object of the present invention to provide an optical device achieving a maximum throughput in a broad frequency range, while maintaining a simple structure.
Thereto the optical device according to the present invention is characterized in that the optical device comprises waveguide device temperature control means having a temperature control input, whereby an optical signal is input to one of the phased array waveguide devices, whose output is coupled to the temperature control input of the temperature control means.
It is an advantage of the optical device according to the invention that one of the arrayed waveguide gratings is applied for temperature control purposes only, while the other grating is used as a flat response main filter for each of the input RF signals concerned. In general temperature control of the gratings is vital, because of the relative strong dependency of the transmission properties on the actual temperature. Temperature control has improved because of the fact that if the transmission of the optical signal, which is input to the one separate arrayed waveguide grating concerned is stabilized relative to the temperature of said grating, the wavelength signals and their transmission through the other grating are automatically stabilized and maximized/centralized as well. A further advantage is that this second grating used for temperature stabilization purposes does not interfere with the first grating or with a proper functioning thereof. The optical signal may be one of the optical wavelength signals or be generated by a reference source, e.g. a reference laser.
Preferably an embodiment of the optical device of the invention is characterized in that the phased array waveguide devices comprise arrayed waveguide gratings coupled between waveguide structures and sharing one substrate. At least seen from the manufacturing side this does not add substantial complexity to the manufacturing thereof.
Another embodiment of the optical device according to the invention is characterized in that the each of the arrayed waveguide gratings comprises waveguides, whereby the number of waveguides of the arrayed waveguide grating for temperature control exceeds the number of waveguides of the other arrayed waveguide grating. Because of the larger number of waveguides in the arrayed waveguide grating for temperature control advantageously the wavelength resolution thereof is larger than that of the other arrayed waveguide grating. As a consequence the former grating is better equipped for temperature control, as the amplitude of the optical signal conveyed thereby is a better representation for the actual temperature of the grating.
A still further embodiment of the optical device according to the invention is characterized in that at least a part of input or output optical waveguide signals is applied to the phased array waveguide device for temperature control. It is an advantage that this opens the way for implementing various practical embodiments of the optical device according to the invention.
In possible different implementations the optical device is further characterized in that the optical device functions as a multiplexer or a demultiplexer.
Similarly the phased array waveguide device for application in the optical device is characterized in that it comprises waveguide structures having separate arrayed waveguide gratings coupled there between.